EFFECT OF SNOW AND FIRN HYDROLOGY ON THE PHYSICAL AND CHEMICAL CHARACTERISTICS OF GLACIAL RUNOFF

Near-surface processes on glaciers, including water flow over bare ice and through seasonal snow and firn, have a significant effect on the speed, volume and chemistry of water flow through the glacier. The transient nature of the seasonal snow profoundly affects the water discharge and chemistry. Water flow through snow is fairly slow compared with flow over bare ice and a thinning snowpack on a glacier decreases the delay between peak meltwater input and peak stream discharge. Furthermore, early spring melt flushes the snowpack of solutes and by mid-summer the melt water flowing into the glacier is fairly clean by comparison. The firn, a relatively constant feature of glaciers, attenuates variations in water drainage into the glacier by temporarily storing water in saturated layer. Bare ice exerts opposite influences by accentuating variations in runoff by water flowing over the ice surface. The melt of firn and ice contributes relatively clean (solute-free) water to the glacier water system.     

Initial results from a distributed,physically based model of glacier hydrology

This paper describes the development and testing of a distributed, physically based model of glacier hydrology. The model is used to investigate the behaviour of the hydrological system of Haut Glacier d'Arolla, Valais, Switzerland. The model has an hourly time-step and three main components: a surface energy balance submodel, a surface flow routing submodel and a subglacial hydrology submodel. The energy balance submodel is used to calculate meltwater production over the entire glacier surface. The surface routing submodel routes meltwater over the glacier surface from where it is produced to where it either enters the subglacial hydrological system via moulins or runs off the glacier surface. The subglacial hydrology submodel calculates water flow in a network of conduits, which can evolve over the course of a melt season simulation in response to changing meltwater inputs. The main model inputs are a digital elevation model of the glacier surface and its surrounding topography, start-of-season snow depth distribution data and meteorological data. Model performance is evaluated by comparing predictions with field measurements of proglacial stream discharge, subglacial water pressure (measured in a borehole drilled to the glacier bed) and water velocities inferred from dye tracer tests. The model performs best in comparison with the measured proglacial stream discharges, but some of the substantial features of the other two records are also reproduced. In particular, the model results show the high amplitude water pressure cycles observed in the borehole in the mid-melt season and the complex velocity/discharge hysteresis cycles observed in dye tracer tests. The results show that to model outflow hydrographs from glacierized catchments effectively, it is necessary to simulate spatial and temporal variations in surface melt rates, the delaying effect of the surface snowpack and the configuration of the subglacial drainage system itself. The model's ability to predict detailed spatial and temporal patterns of subglacial water pressures and velocities should make it a valuable tool for aiding the understanding of glacier dynamics and hydrochemistry. © 1998 John Wiley & Sons, Ltd.     

Seasonal sediment fluxes forcing supraglacial melting on the Wright Lower Glacier,McMurdo Dry Valleys,Antarctica

Cold‐based glaciers exist in low temperature and low humidity environments in which shortwave radiation is the largest source of energy to the glacier surface and the energy budget is very sensitive to the surface albedo. Consequently, the presence of relatively low volumes of debris on glacier surfaces has a significant impact on the timing, magnitude and rate of ablation at the surface. The aim of this study is to understand how the presence of sediment on the glacier surface at the start of the melt season can affect meltwater generation and delivery on a cold‐based glacier. A combination of field measurements, energy balance modelling and chemical mixing modelling were used on the Wright Lower Glacier, McMurdo Dry Valleys, Antarctica, between October 2005 and January 2006 to address this aim. In this system, sediment was transported onto the glacier surface during the winter months (March–October) by foehn winds, which reduced surface albedo at the start of the summer melt season. The areas of the glacier on which sediment accumulated began to melt earlier than other parts of the glacier and experienced a longer melt season. Over the study period, the total ablation on the dirty surfaces was nine times greater than for clean ice. Ablation on the dirty surfaces is dominated by melting, whereas sublimation dominates the clean ice. As the sediment was unevenly distributed over the glacier surface, the variation in melt amount and timing drove the development of a cryoconite hole system. Copyright © 2012 John Wiley & Sons, Ltd.     

Seasonal snowpack dynamics and runoff in a cool temperate forest: lysimeter experiment in Niigata,Japan

Seasonal snowpack dynamics are described through field measurements under contrasting canopy conditions for a mountainous catchment in the Japan Sea region. Microclimatic data, snow accumulation, albedo and lysimeter runoff are given through the complete winter season 2002–03 in (1) a mature cedar stand, (2) a larch stand, and (3) a regenerating cedar stand or opening. The accumulation and melt of seasonal snowpack strongly influences streamflow runoff during December to May, including winter baseflow, mid‐winter melt, rain on snow, and diurnal peaks driven by radiation melt in spring. Lysimeter runoff at all sites is characterized by constant ground melt of 0·8–1·0 mm day⁻¹. Rapid response to mid‐winter melt or rainfall shows that the snowpack remains in a ripe or near‐ripe condition throughout the snow‐cover season. Hourly and daily lysimeter discharge was greatest during rain on snow (e.g. 7 mm h⁻¹ and 53 mm day⁻¹ on 17 December) with the majority of runoff due to rainfall passing through the snowpack as opposed to snowmelt. For both rain‐on‐snow and radiation melt events lysimeter discharge was generally greatest at the open site, although there were exceptions such as during interception melt events. During radiation melt instantaneous discharge was up to 4·0 times greater in the opening compared with the mature cedar, and 48 h discharge was up to 2·5 times greater. Perhaps characteristic of maritime climates, forest interception melt is shown to be important in addition to sublimation in reducing snow accumulation beneath dense canopies. While sublimation represents a loss from the catchment water balance, interception melt percolates through the snowpack and contributes to soil moisture during the winter season. Strong differences in microclimate and snowpack albedo persisted between cedar, larch and open sites, and it is suggested further work is needed to account for this in hydrological simulation models. Copyright © 2005 John Wiley & Sons, Ltd.     

Solute provenance,transport and denudation in a high arctic glacierized catchment

Recent understanding of chemical weathering in glacierized catchments has been focused on mid-latitude, Alpine catchments; comparable studies from the high latitudes are currently lacking. This paper attempts to address this deficiency by examining solute provenance, transport and denudation in a glacierized catchment at 78°N in the Svalbard High Arctic archipelago. Representative samples of snow, glacier ice, winter proglacial icing and glacier meltwater were obtained from the catchment during spring and summer 1993 and analysed for major ion chemistry. Seasonal variations in the composition of glacier meltwater occur and are influenced by proglacial solute acquisition from the icing at the very start of the melt season, and subsequently by a period of discharge of concentrated snowmelt caused by snowpack elution; weathering within the ice-marginal channels that drain the glacier, particularly carbonation reactions, continues to furnish solute to meltwater when suspended sediment concentrations increase later in the melt season. Partitioning the solute flux into its various components (sea-salt, crustal, aerosol and atmospheric sources) shows that c. 25% of the total flux is sea salt derived, consistent with the maritime location of the glacier, and c. 71% is crustally derived. Estimated chemical denudation, 160 meq m⁻² a⁻¹ sea salt-corrected cation equivalent weathering rate, is somewhat low compared with other studied glacierized catchments (estimates in the range 450–1000 meq m⁻² a⁻¹), which is probably attributable to the relatively short melt season and low specific runoff in the High Arctic. A positive relationship was identified between discharge and CO₂ drawdown owing to carbonation reactions in turbid meltwater. © 1997 John Wiley & Sons, Ltd.     

Quantitative evaluation of different hydrological modelling approaches in a partly glacierized Swiss watershed

Mountain water resources management often requires hydrological models that need to handle both snow and ice melt. In this study, we compared two different model types for a partly glacierized watershed in central Switzerland: (1) an energy‐balance model primarily designed for snow simulations; and (2) a temperature‐index model developed for glacier simulations. The models were forced with data extrapolated from long‐term measurement records to mimic the typical input data situation for climate change assessments. By using different methods to distribute precipitation, we also assessed how various snow cover patterns influenced the modelled runoff. The energy‐balance model provided accurate discharge estimations during periods dominated by snow melt, but dropped in performance during the glacier ablation season. The glacier melt rates were sensitive to the modelled snow cover patterns and to the parameterization of turbulent heat fluxes. In contrast, the temperature‐index model poorly reproduced snow melt runoff, but provided accurate discharge estimations during the periods dominated by glacier ablation, almost independently of the method used to distribute precipitation. Apparently, the calibration of this model compensated for the inaccurate precipitation input with biased parameters. Our results show that accurate estimates of snow cover patterns are needed either to correctly constrain the melt parameters of the temperature‐index model or to ensure appropriate glacier surface albedos required by the energy‐balance model. Thus, particularly when only distant meteorological stations are available, carefully selected input data and efficient extrapolation methods of meteorological variables improve the reliability of runoff simulations in high alpine watersheds. Copyright © 2011 John Wiley & Sons, Ltd.     

Effect of snowpack removal on energy balance,melt and runoff in a small supraglacial catchment

Modelling melt and runoff from snow‐ and ice‐covered catchments is important for water resource and hazard management and for the scientific study of glacier hydrology, dynamics and hydrochemistry. In this paper, a distributed, physically based model is used to determine the effects of the up‐glacier retreat of the snowline on spatial and temporal patterns of melt and water routing across a small (0·11 km²) supraglacial catchment on Haut Glacier d'Arolla, Switzerland. The melt model uses energy‐balance theory and accounts for the effects of slope angle, slope aspect and shading on the net radiation fluxes, and the effects of atmospheric stability on the turbulent fluxes. The water routing model uses simplified snow and open‐channel hydrology theory and accounts for the delaying effects of vertical and horizontal water flow through snow and across ice. The performance of the melt model is tested against hourly measurements of ablation in the catchment. Calculated and measured ablation rates show a high correlation (r² = 0·74) but some minor systematic discrepancies in the short term (hours). These probably result from the freezing of surface water at night, the melting of the frozen layer in the morning, and subsurface melting during the afternoon. The performance of the coupled melt/routing model is tested against hourly discharge variations measured in the supraglacial stream at the catchment outlet. Calculated and measured runoff variations show a high correlation (r² = 0·62). Five periods of anomalously high measured discharge that were not predicted by the model were associated with moulin overflow events. The radiation and turbulent fluxes contribute c. 86% and c. 14% of the total melt energy respectively. These proportions do not change significantly as the surface turns from snow to ice, because increases in the outgoing shortwave radiation flux (owing to lower albedo) happen to be accompanied by decreases in the incoming shortwave radiation flux (owing to lower solar incidence angles) and increases in the turbulent fluxes (owing to higher air temperatures and vapour pressures). Model sensitivity experiments reveal that the net effect of snow pack removal is to increase daily mean discharges by c. 50%, increase daily maximum discharges by >300%, decrease daily minimum discharges by c. 100%, increase daily discharge amplitudes by >1000%, and decrease the lag between peak melt rates and peak discharges from c. 3 h to c. 50 min. These changes have important implications for the development of subglacial drainage systems. Copyright © 2002 John Wiley & Sons, Ltd.     

A spreadsheet‐based (Microsoft Excel) point surface energy balance model for glacier and snow melt studies

This paper describes a point surface energy balance model which runs within the Microsoft Excel spreadsheet package. The study incorporates a large amount of previous energy balance work and presents it in a useable form. The core model calculates the net shortwave and longwave radiation fluxes, the turbulent sensible and latent heat fluxes and the surface melt rate at a point on a melting ice or snow surface, from hourly inputs of incoming shortwave radiation, vapour pressure, air temperature and wind speed data. The latitude, longitude, slope angle, aspect, elevation, local temperature lapse rate, albedo and aerodynamic roughness of the study site, and the elevation of the meteorological station, can all be specified in the model. An output file containing the hourly and daily rates, and the totals of the energy fluxes is generated. The main advantages of the model are: first, that it requires only a PC or laptop computer running standard Microsoft Windows software, enabling it to be used at a desktop or in the field; and second, that it can be adapted quickly to different sites, meteorological data formats and other application requirements. Model calculations are compared with measured surface melt rates at five points on Haut Glacier d'Arolla, Switzerland, over a 115 day ablation period. Allowing for differences in shading between the meteorological station and the glacier, the root mean square error of the calculated melt rates is 2·0 mm day⁻¹ water equivalent melt (mean error +1·2 mm day⁻¹), for measured melt rates in the range 23 to 42 mm day⁻¹ water equivalent melt. Copyright © 2000 John Wiley & Sons, Ltd.     

From precipitation to runoff: stable isotopic fractionation effect of glacier melting on a catchment scale

Stable isotope variability and fractionation associated with transformation of precipitation/accumulation to firn to glacial river water is critical in a variety of climatic, hydrological and paleoenvironmental studies. This paper documents the modification of stable isotopes in water from precipitation to glacier runoff in an alpine catchment located in the central Tibetan Plateau. Isotopic changes are observed by sampling firnpack profiles, glacier surface snow/ice, meltwater on the glacier surface and catchment river water at different times during a melt season. Results show the isotopic fractionation effects associated with glacier melt processes. The slope of the δD‐δ¹⁸O regression line and the deuterium excess values decreased from the initial precipitation to the melt‐impacted firnpack (slope from 9.3 to 8.5 and average d‐excess from 13.4‰ to 7.4‰). The slope of the δD‐δ¹⁸O line further decreased to 7.6 for the glacier runoff water. The glacier surface snow/ice from different locations, which produces the main runoff, had the same δD‐δ¹⁸O line slope but lower deuterium excess (by 3.9‰) compared to values observed in the firnpack profile during the melt season. The δD‐δ¹⁸O regression line for the river water exhibited a lower slope compared to the surface snow/ice samples, although they were closely located on the δD‐δ¹⁸O plot. Isotope values for the river and glacier surface meltwater showed little scatter around the δD‐δ¹⁸O regression line, although the samples were from different glaciers and were collected on different days. Results indicate a high consistency of isotopic fractionation in the δD‐δ¹⁸O relationships, as well as a general consistency and temporal covariation of meltwater isotope values at the catchment scale. Copyright © 2013 John Wiley & Sons, Ltd.     

Observations of urban snow properties in Calgary,Canada

Urban winter hydrology has garnered very little attention owing to the general notion that high‐intensity rainfalls are the major flood‐generating events in urban areas. As a result, few efforts have been made to research urban snow and its melt characteristics. This study investigates the characteristics of urban snow that differentiate it from rural snow, and makes recommendations for incorporating these characteristics into an urban snowmelt model. A field study was conducted from the fall of 2001 to the spring of 2002 in the city of Calgary, Canada. Snow depths and densities, soil moisture, soil temperature, snow albedo, net radiation, snow evaporation, and surface temperature were measured at several locations throughout the winter period. The combination of urban snow removal practices and the physical elements that exist in urban areas were found to influence the energy balance of the snowpack profoundly. Shortwave radiation was found to be the main source of energy for urban snow; as a consequence, the albedo of urban snow is a very important factor in urban snowmelt modelling. General observations lead to the classification of snow as one of four types: snow piles, snow on road shoulders, snow on sidewalk edges, and snow in open areas. This resulted in the development of four separate functions for the changing snow albedo values. A study of the frozen ground conditions revealed that antecedent soil moisture conditions had very little impact on frozen ground, and thus frozen ground very nearly always acts as a near impervious area. Improved flood forecasting for urban catchments in cold regions can only be achieved with accurate modelling of urban winter runoff that involves the energy balance method, incorporating snow redistribution and urban snow‐cover characteristics, and using small time steps. Copyright © 2004 John Wiley & Sons, Ltd.     

Incorporating topographic variability into a simple regional snowmelt model

General circulation models (GCMs), or stand‐alone models that are forced by the output from GCMs, are increasingly being used to simulate the interactions between snow cover, snowmelt, climate and water resources. The variation in snowpack extent, and hence albedo, through time in a cell is likely to be substantial, especially in mid‐latitude mountainous regions. As a consequence, the energy budget simulation by a GCM relies on a realistic representation of snowpack extent. Similarly, from a water resource perspective, the spatial extent of the pack is key in predicting meltwater discharges into rivers. In this paper a simple computationally efficient regional snow model has been developed, which is based on a degree‐day approach and simulates the fraction of the model domain covered by snow, the spatially averaged melt rate and the mean snowpack depth. Computational efficiency is achieved through a novel spatial averaging procedure, which relies on the assumptions that precipitation and temperature scale linearly with elevation and that the distribution of elevations in the domain can be modelled by a continuous function. The resulting spatially averaged model is compared with both observations of the duration of snow cover throughout Austria and with results from a distributed model based on the same underlying assumptions but applied at a fine spatial resolution. The new spatially averaged model successfully simulated the seasonal snow duration observations and reproduced the daily dynamics of snow cover extent, the spatially averaged melt rate and mean pack depth simulated by the distributed model. It, therefore, offers a computationally efficient and easily applied alternative to the current crop of regional snow models. Copyright © 2004 John Wiley & Sons, Ltd.     

Seasonal evolution of meltwater generation,storage and discharge at a non‐temperate glacier in Svalbard

In glacierized catchments, meteorological inputs driving surface melting are translated into runoff outputs mediated by the glacier hydrological system: analysis of the relationship between meteorology and diurnal and seasonal patterns of runoff should reflect the functioning of that system, with the role of meltwater storage likely to be of particular importance. Daily meltwater storage is determined for a glacier at 78 °N in the Svalbard archipelago, by comparing inputs calculated from a surface energy balance model with measured outputs (proglacial discharge). Solar radiation, air temperature, wind speed and proglacial discharge are then analysed by regression and time‐series methods, in order to assess the meteorology–discharge relationship and its variation at diurnal and seasonal time‐scales. The recorded discharge time‐series can be divided into two contrasting intervals: up to early August, proglacial discharge was high and variable, mean hydrographs showed little indication of diurnal cycling, ARIMA models of discharge indicated a non‐seasonal, moving‐average generating process, and there was a net loss of meltwater from storage; from early August, proglacial discharge was low and relatively invariable, but with clearer diurnal cycles, regression models of discharge showed substantially improved correlations with air temperature and solar radiation, ARIMA models indicated a non‐seasonal, autoregressive generating process, and eventually a seasonal component, and there was a net gain in meltwater storage. The transition between the two periods is brief compared with the duration of the melt season. The runoff response to meteorology therefore lacks the strongly progressive element previously identified in mid‐latitude glacierized catchments. In particular, the glacier hydrological system only appears responsive to diurnal forcing following the depletion of the seasonal snowpack meltwater store. Copyright © 2001 John Wiley & Sons, Ltd.     

Hydrologic vulnerability to climate change of the Mandrone glacier (Adamello-Presanella group,Italian Alps)

In order to assess the annual mass balance of the Mandrone glacier in the Central Alps an energy-balance model was applied, supported by snowpack, meteorological and glaciological observations, together with satellite measurements of snow covered areas and albedo. The Physically based Distributed Snow Land and Ice Model (PDSLIM), a distributed multi-layer model for temperate glaciers, which was previously tested on both basin and point scales, was applied.Verification was performed with a network of ablation stakes over two summer periods. Satellite images processed within the Global Land Ice Measurements from Space (GLIMS) project were used to estimate the ice albedo and to verify the position of the simulated transient snowline on specific dates. The energy balance was estimated for the Mandrone and Presena glaciers in the Central Italian Alps. Their modeled balances (−1439 and −1503 mm w.e. year⁻¹, respectively), estimated over a 15 year period, are in good agreement with those obtained with the glaciological method for the Caresèr glacier, a WGMS (World Glacier Monitoring Service) reference located in the nearby Ortles-Cevedale group.Projections according to the regional climate model COSMO-CLM (standing for COnsortium for Small-scale MOdeling model in CLimate Mode) indicate that the Mandrone glacier might not survive the current century and might be halved in size by 2050.     

Charred forests accelerate snow albedo decay: parameterizing the post‐fire radiative forcing on snow for three years following fire

As large, high‐severity forest fires increase and snowpacks become more vulnerable to climate change across the western USA, it is important to understand post‐fire disturbance impacts on snow hydrology. Here, we examine, quantify, parameterize, model, and assess the post‐fire radiative forcing effects on snow to improve hydrologic modelling of snow‐dominated watersheds having experienced severe forest fires. Following a 2011 high‐severity forest fire in the Oregon Cascades, we measured snow albedo, monitored snow, and micrometeorological conditions, sampled snow surface debris, and modelled snowpack energy and mass balance in adjacent burned forest (BF) and unburned forest sites. For three winters following the fire, charred debris in the BF reduced snow albedo, accelerated snow albedo decay, and increased snowmelt rates thereby advancing the date of snow disappearance compared with the unburned forest. We demonstrate a new parameterization of post‐fire snow albedo as a function of days‐since‐snowfall and net snowpack energy balance using an empirically based exponential decay function. Incorporating our new post‐fire snow albedo decay parameterization in a spatially distributed energy and mass balance snow model, we show significantly improved predictions of snow cover duration and spatial variability of snow water equivalent across the BF, particularly during the late snowmelt period. Field measurements, snow model results, and remote sensing data demonstrate that charred forests increase the radiative forcing to snow and advance the timing of snow disappearance for several years following fire. Copyright © 2016 John Wiley & Sons, Ltd.     

Influence of melt‐freeze‐cycles on the radionuclide transport in homogeneous laboratory snowpack

Radionuclides released to the environment and deposited with or onto snow can be stored over long time periods if ambient temperature stays low, particularly in glaciated areas or high alpine sites. The radionuclides will be accumulated in the snowpack during the winter unless meltwater runoff at the snow base occurs. They will be released to surface waters within short time during snowmelt in spring. In two experiments under controlled melting conditions of snow in the laboratory, radionuclide migration and runoff during melt‐freeze‐cycles were examined. The distribution of Cs‐134 and Sr‐85 tracers in homogeneous snow columns and their fractionation and potential preferential elution in the first meltwater portions were determined. Transport was associated with the percolation of meltwater at ambient temperatures above 0 °C after the snowpack became ripe. Mean migration velocities in the pack were examined for both nuclides to about 0.5 cm hr^?1 after one diurnal melt‐freeze‐cycle at ambient temperatures of ?2 to 4 °C. Meltwater fluxes were calculated with a median of 1.68 cm hr^?1. Highly contaminated portions of meltwater with concentration factors between 5 and 10 against initial bulk concentrations in the snowpack were released as ionic pulse with the first meltwater. Neither for caesium nor strontium preferential elution was observed. After recurrent simulated day‐night‐cycles (?2 to 4 °C), 80% of both radionuclides was released with the first 20% of snowmelt within 4 days. 50% of Cs‐134 and Sr‐85 were already set free after 24 hr. Snowmelt contained highest specific activities when the melt rate was lowest during the freeze‐cycles due to concentration processes in remaining liquids, enhanced by the melt‐freeze‐cycling. This implies for natural snowpack after significant radionuclide releases, that long‐time accumulation of radionuclides in the snow during frost periods, followed by an onset of steady meltwater runoff at low melt rates, will cause the most pronounced removal of the contaminants from the snow cover. This scenario represents the worst case of impact on water quality and radiation exposure in aquatic environments.     

MELTWATER FLUXES AT AN ARCTIC FOREST-TUNDRA SITE

Models of surface energy balance and snow metamorphism are utilized to predict the energy and meltwater fluxes at an Arctic site in the forest–tundra transition zone of north-western Canada. The surface energy balance during the melt period is modelled using an hourly bulk aerodynamic approach. Once a snowcover becomes patchy, advection from the bare patches to the snow-covered areas results in a large spatial variation in basin snowmelt. In order to illustrate the importance of small-scale, horizontal advection, a simple parameterization scheme using sensible heat fluxes from snow free areas was tested. This scheme estimates the maximum horizontal advection of sensible heat from the bare patches to the snow-covered areas. Calculated melt was routed through the measured snowcover in each landscape type using a variable flow path, meltwater percolation model. This allowed the determination of the spatial variability in the timing and magnitude of meltwater release for runoff. Model results indicate that the initial release of meltwater first occurred on the shallow upland tundra sites, but meltwater release did not occur until nearly two weeks later on the deep drift snowcovers. During these early periods of melt, not all meltwater is available for runoff. Instead, there is a period when some snowpacks are only partially contributing to runoff, and the spatial variation of runoff contribution corresponds to landscape type. Comparisons of melt with and without advection suggests that advection is an important process controlling the timing of basin snowmelt.     

Long-term shifts in feedbacks among glacier surface change,melt generation and runoff,McMurdo Dry Valleys,Antarctica

Glaciers of the McMurdo dry valleys (MDVs) Antarctica are the main source of streamflow in this polar desert. Because summer air temperatures hover near 0°C small changes in the energy balance strongly affect meltwater generation. Here we demonstrate that increased surface roughness, which alters the turbulent transfer of energy between the ice surface and atmosphere, yields a detectable increase in meltwater runoff. At low elevations on the glaciers, basin-like topography became significantly rougher over 13 years between repeat lidar surveys, yielding greater melt. In contrast, the smoother ice at higher elevation exhibited no detectable change in roughness. We pose a conceptual model of the cycle of glacier surface change as a result of climate forcing whereby glacier surfaces transition from being dominated by sublimation to becoming increasingly melt-dominated, which is reversible under prolonged cool periods. This research advances our understanding of warm season effects on polar glaciers.     

Effect of dust event timing on glacier runoff: sensitivity analysis for a Tibetan glacier

The impact of the timing of dust deposition on glacier runoff was evaluated using a glacier mass‐balance model with a newly improved scheme to track a dusted layer in a snow layer of a glacier. The lowering of surface albedo due to the dusted layer appearing leads to a drastic increase of glacier runoff even under the same meteorological conditions. Calculations of seasonal sensitivity, the relationship between dusted date and resulting runoff, have shown that dust deposition during a melting season might cause a drastic mass outflow from a glacier through changing the surface albedo during the melting season. Copyright © 2006 John Wiley & Sons, Ltd.     

Characteristics and climatic sensitivities of runoff from a cold‐type glacier on the Tibetan Plateau

Model calculations are made in order to understand the characteristics and response to climate change of runoff from a cold glacier on the Tibetan Plateau. Some 20% of meltwater is preserved at the snow–ice boundary due to refreezing, since the glaciers in mid to northern Tibet are sufficiently cooled during the previous winter. Sensitivity to alterations in meteorological parameters has revealed that a change in air temperature would cause not only an increase in melting by sensible heat, but also a drastic increase in melting due to lowering of the albedo, since some of the snowfall changes to rainfall. In addition, it was suggested that a decrease in precipitation would cause a lowering of the surface albedo, with a resulting increase in the contribution of glacier runoff to the total runoff of river water. This study shows the first quantitative evaluation of the above effects, though they have been suggested qualitatively. The seasonal sensitivity of glacier runoff was examined by changing the dates given for a meteorological perturbation for a period of only 5 days. It was revealed that changes in both air temperature and precipitation during the melting season strongly affected glacier runoff by changing the surface albedo, though these perturbations only slightly altered the annual averages. Copyright © 2006 John Wiley & Sons, Ltd.     

Modelling the hydrological response of debris‐free and debris‐covered glaciers to present climatic conditions in the semiarid Andes of central Chile

We apply the process‐based, distributed TOPKAPI‐ETH glacio‐hydrological model to a glacierized catchment (19% glacierized) in the semiarid Andes of central Chile. The semiarid Andes provides vital freshwater resources to valleys in Chile and Argentina, but only few glacio‐hydrological modelling studies have been conducted, and its dominant hydrological processes remain poorly understood. The catchment contains two debris‐free glaciers reaching down to 3900 m asl (Bello and Yeso glaciers) and one debris‐covered avalanche‐fed glacier reaching to 3200 m asl (Piramide Glacier). Our main objective is to compare the mass balance and runoff contributions of both glacier types under current climatic conditions. We use a unique dataset of field measurements collected over two ablation seasons combined with the distributed TOPKAPI‐ETH model that includes physically oriented parameterizations of snow and ice ablation, gravitational distribution of snow, snow albedo evolution and the ablation of debris‐covered ice. Model outputs indicate that while the mass balance of Bello and Yeso glaciers is mostly explained by temperature gradients, the Piramide Glacier mass balance is governed by debris thickness and avalanches and has a clear non‐linear profile with elevation as a result. Despite the thermal insulation effect of the debris cover, the mass balance and contribution to runoff from debris‐free and debris‐covered glaciers are similar in magnitude, mainly because of elevation differences. However, runoff contributions are distinct in time and seasonality with ice melt starting approximately four weeks earlier from the debris‐covered glacier, what is of relevance for water resources management. At the catchment scale, snowmelt is the dominant contributor to runoff during both years. However, during the driest year of our simulations, ice melt contributes 42 ± 8% and 67 ± 6% of the annual and summer runoff, respectively. Sensitivity analyses show that runoff is most sensitive to temperature and precipitation gradients, melt factors and debris cover thickness. Copyright © 2016 John Wiley & Sons, Ltd.